Systems and methods for the on-board catalytic production of hydrogen from ammonia using a heat exchange catalyst unit and an electric catalyst unit operating in series

ABSTRACT

The present invention relates, in general, to systems and methods for generating hydrogen from ammonia on-board vehicles, where the produced hydrogen is used as fuel source for an internal combustion engine. The present invention utilizes an electric catalyst unit operating in series with a heat exchange catalyst unit. The electric catalyst unit is used to initiate an ammonia cracking process on-board during a cold start or low load operating condition of the internal combustion engine, where the ammonia cracking process occurs in the heat exchange catalyst unit once exhaust gas from the internal combustion engine has been heated to a threshold temperature suitable to perform the ammonia cracking process.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Non-Provisional patentapplication Ser. No. 17/986,265 entitled “SYSTEMS AND METHODS FOR THECATALYTIC PRODUCTION OF HYDROGEN FROM AMMONIA ON-BOARD MOTOR VEHICLES”filed on Nov. 14, 2022, which claims the benefit of U.S. ProvisionalPatent Application No. 63/395,820 entitled “SYSTEMS AND METHODS FOR THECATALYTIC PRODUCTION OF HYDROGEN FROM AMMONIA ON-BOARD MOTOR VEHICLES”filed on Aug. 6, 2022, U.S. Provisional Patent Application No.63/355,959 entitled “SYSTEMS AND METHODS FOR THE CATALYTIC PRODUCTION OFHYDROGEN FROM AMMONIA ON-BOARD MOTOR VEHICLES” filed on Jun. 27, 2022,and U.S. Provisional Patent Application No. 63/312,121 entitled “SYSTEMSAND METHODS FOR THE CATALYTIC PRODUCTION OF HYDROGEN FROM AMMONIAON-BOARD MOTOR VEHICLES” filed on Feb. 21, 2022, all of which arecommonly owned, the disclosure of each is incorporated herein byreference in their entireties.

BACKGROUND Field of the Invention

The present invention relates, in general, to systems and methods forgenerating hydrogen from ammonia on-board vehicles, where the producedhydrogen is used as fuel source for an internal combustion engine.

Description of Related Art

The increase in the overall temperature on and above Earth's surfacerepresents a critical challenge facing the planet. Earth's climate issignificantly changing mainly due to human activities, and thetransportation sector plays a prominent role in this global warming. Forexample, internal combustion engines have traditionally burned fossilfuels, which in turn produces CO₂, a known contributor to globalwarming. Over the last decade, the transportation sector has madestrides in making electric- and hybrid-powered vehicles available on amass scale. Generally speaking, most electric and hybrid vehicles soldtoday tend to produce significantly fewer global warming emissions thanmost vehicles operating on fossil fuels, namely gasoline. However, theenvironmental benefits of electric and hybrid vehicles still dependprimarily on how much fossil fuel is being burned to charge thesevehicles. For example, if the vehicles are charged using a coal-heavypower grid, the environmental benefits are lessened.

Furthermore, the batteries and fuel cells in electrified vehicles relyon raw materials such as cobalt, lithium and rare earth elements. Thesematerials have been linked to grave environmental and human rightsconcerns. For instance, cobalt has been especially problematic. Miningcobalt produces hazardous tailings and slags that can leach into theenvironment, and studies have found high exposure rates of cobalt andother metals in communities surrounding cobalt mining and processingfacilities. Extracting such metals from their ores also requires aprocess called smelting, which can emit sulfur oxide and other harmfulair pollution.

Given the sustained environmental issues that currently exist withelectrified vehicles, ammonia has been suggested as an alternative tofossil fuels for use in internal combustion engines, given itsrelatively high energy density and zero CO₂ emissions when combusted.However, pure ammonia cannot efficiently be used as a fuel in smallinternal combustion engines, whether spark-ignited (i.e., gasoline), orcompression ignited (i.e., diesel), because pure ammonia burns tooslowly to complete combustion during the power stroke in a four-strokeengine operating at speeds of thousands of revolutions per minute (RPM).In other words, when ammonia is combusted, the combustion produces aflame with a relatively low propagation speed. This low combustion rateof ammonia causes combustion to be inconsistent under low engine loadand high engine speed operating conditions.

Prior approaches to fueling combustion engines with ammonia haverequired mixing ammonia with a secondary combustion promoter fuel, suchas gasoline, liquefied petroleum, or diesel. However, the requirementfor a secondary combustion promoter fuel fluctuates with varying engineloads and engine speed, which can cause control issues. Thus, using asecondary combustion promotor fuel typically requires an additionalcontrol mechanism that must be part of the engine management system.

Hydrogen has also been suggested as an alternative to fossil fuels foruse in internal combustion engines, as it is extremely plentiful, andcan match the power of gasoline or diesel given its lower heating value.Hydrogen has a high flame velocity and a low ignition temperature,making it easy to ignite, and it is known to burn approximately sixtimes faster than gasoline. Most importantly, hydrogen produces zero CO₂emissions when combusted.

However, a challenge with using hydrogen on-board a vehicle is that itis an extremely light, low-density gas, and it cannot be stored aseasily as liquid fossil fuels. Hydrogen requires compression, cooling,or a combination of both. The use of compressed hydrogen fuel tankson-board vehicles inherently leads to a number of safety issues, such asthe risk of potential failure of the pressure vessel, leakage ofhydrogen in a confined space, and the like.

It is known that hydrogen can be obtained from ammonia by catalyticdecomposition into its constituent hydrogen and nitrogen componentsthrough a process referred to as “cracking”. However, the ammoniacracking process is an endothermic process which requires heat. With alimited electrical supply on-board a motor vehicle, it is difficult togenerate the heat required to efficiently perform the ammonia crackon-board.

Therefore, there is a need for systems and methods to generate hydrogenfrom ammonia on-board vehicles for use as an internal combustion enginefuel source which addresses the aforementioned challenges and drawbacksof electrified vehicles, ammonia-fueled internal combustion engines, andthe on-board storage of hydrogen for hydrogen fueled internal combustionengines.

SUMMARY

In an embodiment, the present invention is directed to a system foron-board ammonia cracking for an internal combustion engine, comprising:an ammonia tank containing liquid ammonia; a heat exchange catalyst unitfluidly coupled to the ammonia tank, wherein the heat exchange catalystunit receives exhaust gas from the internal combustion engine; and anelectric catalyst unit fluidly coupled in series to the heat exchangecatalyst unit, wherein gaseous ammonia flows from the ammonia tank tothe heat exchange catalyst unit upon vaporization of the liquid ammonia,wherein the gaseous ammonia undergoes a cracking process in the heatexchange catalyst unit if the exhaust gas has reached a temperaturesufficient to perform ammonia cracking, and wherein the gaseous ammoniaexits the heat exchange catalyst unit and flows to the electric catalystunit and undergoes the cracking process in the electric catalyst unit ifthe exhaust gas has not reached a temperature sufficient to performammonia cracking,

In another embodiment, the present invention is directed to a system foron-board ammonia cracking for an internal combustion engine, comprising:an ammonia tank containing ammonia; a heat exchange catalyst unitfluidly coupled to the ammonia tank, wherein the heat exchange catalystunit receives exhaust gas from the internal combustion engine andreceives the ammonia from the ammonia tank; and an electric catalystunit fluidly coupled in series to the heat exchange catalyst unit, theelectric catalyst unit including an electric heater, wherein the ammoniaundergoes a cracking process in the heat exchange catalyst unit if theexhaust gas has reached a temperature sufficient to perform ammoniacracking, wherein the ammonia exits the heat exchange catalyst unit andflows to the electric catalyst unit and undergoes the cracking processin the electric catalyst unit if the exhaust gas has not reached atemperature sufficient to perform ammonia cracking, and wherein hydrogenresulting from the cracking process flows to the internal combustionengine.

In yet another embodiment, the present invention is directed to a systemfor on-board ammonia cracking for an internal combustion engine,comprising: an ammonia tank containing ammonia; a heat exchange catalystunit fluidly coupled to the ammonia tank, wherein the heat exchangecatalyst unit receives exhaust gas from the internal combustion engineand receives the ammonia from the ammonia tank; and an electric catalystunit fluidly coupled in series to the heat exchange catalyst unit, theelectric catalyst unit powered using a vehicle power system, wherein theammonia undergoes a cracking process in the heat exchange catalyst unitif the exhaust gas has reached a temperature sufficient to performammonia cracking, and if the exhaust gas has not reached a temperaturesufficient to perform ammonia cracking: (1) the ammonia is pre-heated inthe heat exchange catalyst unit, (2) the pre-heated ammonia exits theheat exchange catalyst unit and flows to the electric catalyst unit, and(3) the pre-heated ammonia undergoes the cracking process in theelectric catalyst unit.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other embodiments of the present invention will be discussedwith reference to the following exemplary and non-limitingillustrations, in which like elements are numbered similarly, and where:

FIG. 1 is a perspective internal view of an exchange catalyst unit thatutilizes a TPMS

structure;

FIG. 2 is a perspective internal view of the heat exchange catalyst unitthat utilizes a TPMS structure which depicts the flow of heated exhaustgas and gaseous ammonia through the matrix;

FIG. 3 is a perspective view of the matrix having a gyroid TPMSstructure;

FIG. 4 is a perspective view of the matrix having an orthogonal holeTPMS structure;

FIG. 5 is a perspective view of the matrix having a split pea TPMSstructure;

FIG. 6 is a top-down perspective view of the heat exchange catalyst unitthat utilizes a TPMS structure;

FIG. 7 is a front cross-sectional view of a cylindrical heat exchangecatalyst unit that utilizes a TPMS structure;

FIG. 8 is a front cross-sectional view of the cylindrical heat exchangecatalyst unit that utilizes a TPMS structure which depicts the flow ofheated exhaust gas and gaseous ammonia through the matrix;

FIG. 9 is a side cross-sectional view of the cylindrical heat exchangecatalyst unit that utilizes a TPMS structure which depicts the flow ofheated exhaust gas and gaseous ammonia through the matrix;

FIG. 10 is a perspective view of a heat exchange catalyst unit thatutilizes a tube bundle structure;

FIG. 11 is a front cross-sectional view of the heat exchange catalystunit that utilizes a tube bundle structure;

FIG. 12 is a side cross-sectional view of the heat exchange catalystunit that utilizes a tube bundle structure;

FIG. 13 is a front cross-sectional view of a two-pass heat exchangecatalyst unit that utilizes a tube bundle structure;

FIG. 14 is a block diagram of an on-board ammonia cracking system for aninternal combustion engine; and

FIG. 15 is a perspective view of an on-board ammonia cracking system foran internal combustion engine;

FIG. 16 is a top-down perspective view of the on-board ammonia crackingsystem;

FIG. 17 is a perspective side view of the on-board ammonia crackingsystem;

FIG. 18 is a perspective view of an electric catalyst unit; and

FIG. 19 is a cross-sectional view of an electric catalyst unit.

DEFINITIONS

The following definitions are meant to aid in the description andunderstanding of the defined terms in the context of the presentinvention. The definitions are not meant to limit these terms to lessthan is described throughout this specification. Such definitions aremeant to encompass grammatical equivalents.

As used herein, the term “motor vehicle” refers to any moving vehiclethat is capable of carrying one or more human occupants and/or cargo, orwhich is capable of performing a task, and which is powered by any formof energy. The term “motor vehicle” includes, but is not limited to: (a)vehicles such as cars, trucks, vans, minivans, sport utility vehicles,passenger carrying vehicles, goods carrying vehicles, 2-, 3-, and4-wheeled vehicles, quadricycles, motorcycles, scooters, all-terrainvehicles, utility task vehicles, and the like; (b) airborne vehiclessuch as helicopters, airplanes, airships, drones, aerospace vehicles,and the like; (c) marine vessels such as dry cargo ships, liquid cargoships, specialized cargo ships, tug-boats, cruise ships, recreationalboats, fishing boats, personal watercraft, jet skis, and the like; (d)locomotives; and (e) heavy equipment and machinery, power generators,lawnmowers and tractors, agricultural equipment and machinery, forestryequipment and machinery, construction equipment and machinery, miningequipment and machinery, and the like.

As used herein, the term “internal combustion engine” refers to anyengine, spark ignition gasoline engine, compression ignition dieselengine, rotary, reciprocating, or other engine wherein combustion takesplace in a combustion chamber, such that the products of combustion,together with any other by-products, perform work by exerting force on amoving surface from which the mechanical output is obtained from theengine. The term “internal combustion engine” includes, but is notlimited to, hybrid internal combustion engines, two-stroke engines,four-stroke engines, six-stroke engines, and the like.

As used herein, the term “catalyst” refers to a material that promotes achemical reaction. The term “catalyst” includes, but is not limited to,a catalyst or catalysts capable of promoting cracking reactions, such asammonia cracking reactions, whether used as base catalyst(s) and/oradditive catalyst(s). The catalyst, for the purposes of the presentinvention, can include, but is not limited to, a non-stoichiometriclithium imide, nickel, iron, cobalt, iron cobalt, ruthenium, vanadium,palladium, rhodium, platinum, sodium amide, and the like, as well asvarious combinations thereof.

As used herein, the term “cracking” refers to a process or processes bywhich ammonia is decomposed into constituent hydrogen and nitrogencomponents over at least one catalyst.

As used herein, the term “nickel alloy” refers to pure nickel or analloy containing nickel as a main component. The term “nickel alloy”includes, but is not limited to, Inconel® 625, Inconel® 718, Inconel®725, and other compound metals having nickel as a main component.Inconel® is the trademark of Special Metals Corporation of Huntington,West Virginia.

As used herein the term “triply-periodic minimal surface (IPMS)” refersto mathematically defined structures that repeat in three dimensionswith zero mean curvatures and large surface areas.

DETAILED DESCRIPTION

It should be understood that aspects of the present invention aredescribed herein with reference to the figures, which show illustrativeembodiments. The illustrative embodiments herein are not necessarilyintended to show all embodiments in accordance with the invention, butrather are used to describe a few illustrative embodiments. Thus,aspects of the invention are not intended to be construed narrowly inview of the illustrative embodiments. In addition, although the presentinvention is described with respect to its application for an internalcombustion engine for a motor vehicle, it is understood that the systemcould be implemented in any engine-driven setting that may be powered byammonia and/or hydrogen fuel.

FIG. 1 is a perspective internal view of a heat exchange catalyst unitthat utilizes a TPMS structure, and which serves as a heat exchanger aswell as a catalytic converter that performs ammonia cracking. The heatexchange catalyst unit 100 is metallic, and in an embodiment, includes agaseous ammonia inlet 102, a hydrogen outlet 104, a heated exhaust gasinlet 106, and an exhaust gas outlet 108. In an embodiment, the heatexchange catalyst unit 100 is made from a nickel alloy. In a preferredembodiment, the heat exchange catalyst unit 100 is made from Inconel®625.

In an embodiment, the gaseous ammonia inlet 102, the hydrogen outlet104, the heated exhaust gas inlet 106, and the exhaust gas outlet 108can be made from the same metallic material as the heat exchangecatalyst unit 100. In another embodiment, the gaseous ammonia inlet 102,the hydrogen outlet 104, the heated exhaust gas inlet 106, and theexhaust gas outlet 108 can be made from stainless steel, silver, bronze,and comparable alloys.

Positioned between the inlets 102, 106 and outlets 104, 108 is a matrix110. The matrix 110 is formed from width-wise surfaces 112 andlength-wise surfaces 114 which run generally perpendicular to eachother. The surfaces 112, 114 of the matrix 110 create passages thatallow the gaseous ammonia and heated exhaust gas to flow; these passagesare indicated by the ammonia channels 116 and heated exhaust gaschannels 118. Gaseous ammonia is supplied to heat exchange catalyst unit100 via inlet 102, while heated exhaust gas is concurrently supplied toinlet 106. The gaseous ammonia traverses the matrix 110 via ammoniachannels 116, while the heated exhaust gas traverses the matrix viaheated exhaust gas channels 118. The ammonia channels 116 and the heatedexhaust gas channels 118 are orientated in a generally perpendicularfashion to one another, such that the gaseous ammonia traverses thematrix 110 at approximate right angles relative to the heated exhaustgas.

In an embodiment, the surfaces 112, 114 have a thickness of 1 to 2millimeters, and each of the surfaces 112, 114 can have the samethickness. In another embodiment, the surfaces 112, 114 can each have adifferent thickness. In yet another embodiment, the surfaces 112, 114may vary in thickness as they each traverse across the matrix 110. Forexample, the surfaces 112, 114 may not have a uniform thickness acrossthe width of the matrix 110, and may have thicker or narrower portionsat various locations.

As shown in FIG. 1 , the matrix 110 physically separates the gasespassing through each of the channels 116, 118, thereby providing anexceptionally large surface area throughout the matrix 110 where theheated exhaust gas exchanges its heat with the gaseous ammonia. In anembodiment, the surfaces 112, 114 of the matrix 110 are coated with acatalyst that facilitates the cracking of ammonia into constituenthydrogen and nitrogen components. In this embodiment, the surfaces 112,114 of the matrix 110 are coated with the catalyst using a washcoatingor deposition technique to bind or adhere the catalyst to the surfaces112, 114.

In another embodiment, catalyst in the form of discrete catalyst mediais deposited into the passages forming the ammonia channels 116 andheated exhaust gas channels 118. The discrete catalyst media can beporous, allowing the gaseous ammonia and exhaust gas to pass through thecatalyst as they each flow through the matrix 110.

In yet another embodiment, the surfaces 112, 114 of the matrix 110 canbe coated with a catalyst as described herein, and additional discretecatalyst media can be deposited into the passages forming the ammoniachannels 116 and heated exhaust gas channels 118.

In an embodiment, the matrix 110 is metallic, and is made from a nickelalloy. In a preferred embodiment, the matrix 110 is made from Inconel®625. The heat exchange catalyst unit 100 and matrix 110 may beconstructed from the same metallic material. In another embodiment, theheat exchange catalyst unit 100 and matrix 110 can be constructed fromdifferent metallic materials.

The material(s) selected for the heat exchange catalyst unit 100 andmatrix 110 need to have the ability to withstand the corrosiveenvironment resulting from the high-temperature heated exhaust gas, aswell as the heated hydrogen gas which is generated from the cracking ofammonia.

In a preferred embodiment, the matrix 110 is in the form of atriply-periodic minimal surface (TPMS), and the matrix 110 isthree-dimensionally (3D) printed using powdered metal. The 3D printingprocess is an additive manufacturing process that uses laser sinteringto selectively fuse together particles of the powdered metal into a TPMSstructure in a layer-by-layer strategy. The TPMS structure of the matrix110 provides for a relatively large surface area comprising cells whichcan be confined within the dimensions and shape of the heat exchangecatalyst unit 100.

The TPMS structure can take on a variety of crystalline-like structureswhich have different patterns and profiles. In the embodiment shown inFIG. 1 , the TPMS is a gyroid structure. The structures can be in theform of, but are not limited to, gyroid, diamond, orthogonal holes,split pea, among many others. Each of these forms has a differentsurface area. For example, in the embodiment shown in FIG. 1 , the heatexchange catalyst unit 100 has dimensions of approximately 10×10×4inches. For a matrix 110 which fits within these dimensions, Table 1provides approximate surface area values for the various TPMS structurethat may be utilized:

TABLE 1 Structure Surface Area (million millimeters²) Gyroid 1.5 millionmm² Orthogonal holes 1.6 million mm² Split pea 2.1 million mm² Diamond2.5 million mm²

It is noted however, that the values in Table 1 are illustrativeexamples only and are not intended to be in any way limiting. Theindividual cell sizes of the TPMS can be modified to increase ordecrease the surface area of the matrix 110. For example, within thesame volume of the heat exchange catalyst unit 100, the individual cellsize can be increased to increase the overall surface area of the matrix110, and conversely, the individual cell size can be decreased todecrease the overall surface area of the matrix 110.

The TPMS structure is ideal for the matrix 110 as it allows heat to bedistributed to all surfaces of the matrix 100, thereby facilitating thechemical reaction required for the ammonia cracking process. As thesurface area of the matrix 110 increases, there is an inherent challengein cleaning the surfaces of the matrix 110 after it is printed, giventhat the formation of the channels 116, 118 become narrower relative toone another as the surface area increases. However, as the cell size ofthe matrix 110 increases, the surface area decreases, which decreasesthe throughput efficiency of the heat exchange catalyst unit 100. Thesurface area of the matrix 110 can depend on the power requirements ofthe motor vehicle and its engine.

In an embodiment, the heat exchange catalyst unit 100 is sized anddimensioned to accommodate a matrix 110 with sufficient surface area tofacilitate the cracking process, while still having a form factor thatis suitable for placement within a motor vehicle. The dimensions of theheat exchange catalyst unit 100 can vary, and can range from 5 to 30inches in width, 5 to 30 inches in length, and 0.5 to 12 inches inheight.

In an embodiment, the heat exchange catalyst unit 100 has a generallysquare shape which accommodates a square-shaped matrix 110, as shown inFIG. 1 , which is an illustrative example only and is not intended to bein any way limiting. In other embodiments, the heat exchange catalystunit 100 can be any polygonal shape, such as, for example, oval, oblong,triangular, square, kite-shaped, trapezoid, parallelogram, rhombus, andthe like, as well as various 3D shapes such as, for example, cube,cuboid, sphere, cone, and the like.

In an embodiment, the ammonia inlet 102 has a smaller diameter than theheated exhaust gas inlet 106, as the exhaust gas flow rate may be ordersof magnitude higher than the ammonia flow rate. As with the dimensionsof the heat exchange catalyst unit 100, the diameters, shape, and sizesof the inlets 102, 106, and outlets 104, 108 can vary based on the powerrequirements of the motor vehicle and its engine.

FIG. 2 is a perspective internal view of the heat exchange catalyst unit100 that utilizes a TPMS structure which depicts the flow of heatedexhaust gas and gaseous ammonia through the matrix. In operation,gaseous ammonia 200 is supplied to the inlet 102 and flows through theammonia channels 116, while heated exhaust gas 202 is concurrentlysupplied to the inlet 106 and flows through the heated gas channels 118.The heated exhaust gas 202 heats the catalyst, resulting in cracking ofthe gaseous ammonia 200 into constituent hydrogen and nitrogencomponents 204. The resulting hydrogen and nitrogen components 204 exitthe heat exchange catalyst unit 100 via the outlet 104 and are suppliedto the downstream injection system for the engine, while residualexhaust gas 206 exits the heat exchange catalyst unit via the outlet108.

FIG. 3 is a perspective view of the matrix 110 having a gyroid TPMSstructure, FIG. 4 is a perspective view of the matrix 110 having anorthogonal hole TPMS structure, and FIG. 5 is a perspective view of thematrix 110 having a split pea TPMS structure. It is noted however, thatthe TPMS structures depicted in FIGS. 1 through 5 are illustrativeexamples only and are not intended to be in any way limiting.

FIG. 6 is a top-down perspective view of the heat exchange catalyst unit100 that utilizes a TPMS structure. In an embodiment, the heat exchangecatalyst unit 100 can be manufactured via welding the inlets 102, 106and outlets 104, 108 to a housing 600. In an embodiment, the housing 600can include a cover (not depicted in FIG. 6 ) which can be removed inorder to service or replace the matrix 110. In another embodiment, theinlets 102, 106 and/or the outlets 104, 108 can be removably attached tothe housing 600 so that different inlets and outlets having variousdimensions, sizes, and flow properties can be utilized with the housing600 in a modular fashion.

FIG. 7 is a front cross-sectional view of a cylindrical heat exchangecatalyst unit 700 that utilizes a TPMS structure. Similar to the heatexchange catalyst unit 100 shown in FIG. 1 , the cylindrical heatexchange catalyst unit 700 is metallic and made from a nickel alloy, andin a preferred embodiment, the cylindrical heat exchange catalyst unit700 is made from Inconel® 625.

In an embodiment, the cylindrical heat exchange catalyst unit 700includes an ammonia inlet 702, a hydrogen outlet 704, a heated exhaustgas inlet 706, and an exhaust gas outlet 708. Positioned between theinlets 702, 706 and outlets 704, 708 is a matrix 710. The matrix 710 isformed from width-wise surfaces 712 and length-wise surfaces 714 whichrun generally perpendicular to each other. The surfaces 712, 714 of thematrix 710 create passages allowing the gaseous ammonia and heatedexhaust gas to flow; these passages are indicated by the ammoniachannels 716 and heated exhaust gas channels 718.

Gaseous ammonia is supplied to cylindrical heat exchange catalyst unit700 via inlet 702, while heated exhaust gas is concurrently supplied toinlet 706. The gaseous ammonia traverses the matrix 710 axially, whilethe heated exhaust gas traverses the matrix laterally.

As shown in FIG. 7 , the matrix 710 physically separates the gasespassing through each of the channels 716, 718, thereby providing anexceptionally large surface area throughout the matrix 710 where theheated exhaust gas exchanges its heat with the gaseous ammonia. In anembodiment, the surfaces 712, 714 of the matrix 710 are coated with acatalyst that facilitates the cracking of ammonia into constituenthydrogen and nitrogen components. In this embodiment, the surfaces 712,714 of the matrix 710 are coated with the catalyst using a washcoatingor deposition technique to bind or adhere the catalyst to the surfaces712, 714.

In another embodiment, catalyst in the form of discrete catalyst mediais deposited into the passages forming the ammonia channels 716 andheated exhaust gas channels 718.

In yet another embodiment, the surfaces 712, 714 of the matrix 710 canbe coated with a catalyst as described herein, and additional discretecatalyst media can be deposited into the passages forming the ammoniachannels 716 and heated exhaust gas channels 718.

FIG. 8 is a front cross-sectional view of the cylindrical heat exchangecatalyst unit 700 that utilizes a TPMS structure which depicts the flowof heated exhaust gas and gaseous ammonia through the matrix. Inoperation, gaseous ammonia 200 is supplied to the inlet 702 and flowsthrough the ammonia channels 716, while heated exhaust gas 202 isconcurrently supplied to the inlet 706 and flows through the heated gaschannels 718. The heated exhaust gas 202 heats the catalyst, resultingin cracking of the ammonia 200 into constituent hydrogen and nitrogencomponents 204. The resulting hydrogen and nitrogen components 204 exitthe heat exchange catalyst unit 700 via the outlet 704 and are suppliedto the downstream injection system for the engine, while residualexhaust gas 206 exits the heat exchange catalyst unit via the outlet708.

FIG. 9 is a side cross-sectional view of the cylindrical heat exchangecatalyst unit 700 that utilizes a TPMS structure which depicts the flowof heated exhaust gas and gaseous ammonia through the matrix. As shownin FIG. 9 , the surfaces 712, 714 of the matrix 710 creates ammoniachannels 716 and heated exhaust gas channels 718. The cylindrical designcan provide efficiencies for mass production, given the rounded parts,fewer welded seams/joints compared to square and rectangular designs,and less susceptibility to thermal stress.

It is noted that cylindrical shape of the cylindrical heat exchangecatalyst unit 700 is an illustrative example only and is not intended tobe in any way limiting. In other embodiments, the heat exchange catalystunit 700 can be any polygonal shape, such as, for example, oval, oblong,triangular, square, kite-shaped, trapezoid, parallelogram, rhombus, andthe like, as well as various 3D shapes such as, for example, cube,cuboid, sphere, cone, and the like.

FIG. 10 is a perspective view of a heat exchange catalyst unit 1000 thatutilizes a tube bundle structure, and which serves as a heat exchangeras well as a catalytic converter that performs ammonia cracking. Theheat exchange catalyst unit 1000 is metallic, and in an embodiment,includes a sidewall 1002 that includes a gaseous ammonia inlet 1004. Inan embodiment, the inlet sidewall 1002 can include additional ports 1006that may be used for a variety of functions. For example, the ports 1006may serve an inlets, or may be coupled to equipment for temperature,throughput, and/or pressure sensing.

The heat exchange catalyst unit 1000 further includes a heated gas inlet1008. In an embodiment, the heated exhaust gas inlet 1008 includes adivider 1010 which spreads the heated exhaust gas from the engine evenlyover the internal tube bundle structure contained within the heatexchange catalyst unit 1000, as described in more detail with referenceto FIG. 11 . In an embodiment, the divider 1010 can have a grid orlattice structure.

The heat exchange catalyst unit 1000 includes an exhaust gas outlet 1012positioned opposite the heated gas inlet 1008.

FIG. 11 is a front cross-sectional view of the heat exchange catalystunit 1000 that utilizes a tube bundle structure. In an embodiment, atube bundle structure 1100 is disposed within the heat exchange catalystunit 1000. The tube bundle structure 1100 is comprised of individualtubes 1102 which extend along the width of the heat exchange catalystunit 1000 from the sidewall 1002, perpendicular to the inlet 1008 andoutlet 1012.

In an embodiment, the tube bundle structure 1100 includes rows and/orcolumns of tubes 1102 arranged in an offset fashion so that eachadjacent row and/or column includes tubes which are offset from itsneighboring tubes. This pattern maximizes the surface area contacted bythe heated exhaust gas as the gas traverses the tube bundle structure1100, thereby maximizing the amount of catalyst heated in order tofacilitate the cracking process.

In an embodiment, the heat exchange catalyst unit 1000 includes at leastone support structure 1104 which facilitates the 3D printing process,and further provide stability against thermal stress during operation ofthe heat exchange catalyst unit 1000.

Gaseous ammonia is supplied to the heat exchange catalyst unit 1000 viainlet 1004, while heated exhaust gas concurrently is supplied to theinlet 1008. The gaseous ammonia traverses the lateral spaces between thetubes 1102, while the heated exhaust gas traverses the axial spaceinside the tubes 1102.

In an embodiment, the spaces between the tubes 1102 are filled with acatalyst in the form of a discrete catalyst media. In anotherembodiment, the tubes 1102 themselves are hollow and are also filledwith the discrete catalyst media.

In yet another embodiment, the external surfaces and/or the internalsurfaces of the tubes 1102 are also coated with the catalyst using awashcoating or deposition technique to bind or adhere the catalyst tothe surfaces.

FIG. 12 is a side cross-sectional view of the heat exchange catalystunit 1000 that utilizes a tube bundle structure 1100. In an embodiment,the heat exchange catalyst unit 1000 includes a sidewall 1200 positionedopposite the sidewall 1002. The sidewall 1200 includes a hydrogen outlet1202, and can include additional ports 1204 that may be used for avariety of functions. For example, the ports 1204 may serve as outlets,or may be coupled to equipment for temperature, throughput, and/orpressure sensing.

In operation, gaseous ammonia is supplied to the inlet 1004, whileheated exhaust gas is concurrently supplied to the inlet 1008. Theheated exhaust gas heats the catalyst, resulting in cracking of theammonia into constituent hydrogen and nitrogen components. The resultinghydrogen and nitrogen components exit the heat exchange catalyst unit1000 via the outlet 1202 and are supplied to the downstream engine.

In an embodiment, the heat exchange catalyst unit 1000 is made from anickel alloy. In a preferred embodiment, the heat exchange catalyst unit1000 is made from Inconel® 625.

In an embodiment, the sidewalls 1002, 1200, the gaseous ammonia inlet1004, the hydrogen outlet 1202, the heated exhaust gas inlet 1008, thedivider 1010, the exhaust gas outlet 1012, and the support structures1104 can be made from the same metallic material as the heat exchangecatalyst unit 1000. In another embodiment, the sidewalls 1002, 1200, thegaseous ammonia inlet 1004, the divider 1010, the hydrogen outlet 1202,the heated exhaust gas inlet 1008, and the exhaust gas outlet 1012 canbe made from stainless steel, silver, bronze, and comparable alloys.

FIG. 13 is a front cross-sectional view of a two-pass heat exchangecatalyst unit 1300 that utilizes a tube bundle structure 1100. In thisembodiment, the support structure 1302 includes a fascia that receives asidewall (not depicted in FIG. 13 ). The support structure 1302 includesa divider 1304 which physically separates the tube bundle structure 1100into a left section 1306 and right section 1308. The divider 1304extends along the width of the two-pass heat exchange catalyst unit 1300between the two sidewalls. In this embodiment, a gaseous ammonia inletis positioned on a sidewall covering the left section 1306, and ahydrogen outlet is positioned on a sidewall covering the right section1308.

In operation, gaseous ammonia is supplied to the gaseous ammonia inlet,while heated exhaust gas is concurrently supplied to the inlet 1008. Asthe ammonia traverses the left section 1306 of tube bundle structure1100, heated exhaust gas heats the catalyst, resulting in cracking ofthe ammonia into constituent hydrogen and nitrogen components. Theremaining ammonia traverses back through the right section 1308 of thetube bundle structure 1100 and continues to undergo cracking, therebyproviding a two-pass cracking process. The resulting hydrogen andnitrogen components exit the two-pass heat exchange catalyst unit 1300via the hydrogen outlet and are supplied to the downstream engine.

FIG. 14 is a block diagram of an on-board ammonia cracking system for aninternal combustion engine. The on-board ammonia cracking system 1400provides a mechanism to generate hydrogen from ammonia which eliminatesthe need for a separate hydrogen tank to be carried by the motorvehicle.

Referring FIG. 14 , an ammonia liquid tank 1402 is mounted to a motorvehicle or engine, and in an embodiment, the ammonia liquid tank 1402can be coupled to a pump 1404. In an embodiment, the tank 1402 isrefillable and/or replaceable. The pump 1404 can be coupled to a port onthe tank 1402 to facilitate the delivery of ammonia from the tank 1402.For example, in a cold environment where the temperature isapproximately 0° C. or less, the vapor pressure of ammonia is notadequate to push itself out of the tank 1402. Thus, the pump 1404 isrequired to draw or force the ammonia out of the tank 1402.

In another embodiment, an electrical heater (not depicted in FIG. 14 )can be coupled to the tank 1402, such as within the tank 1402 or on anouter surface of the tank 1402, in order to heat the liquid ammoniacontained within the tank 1402 to a temperature where it vaporizes intoa gaseous form.

In an embodiment, a pressure regulator 1406 is coupled to an outlet ofthe tank 1402, and serves to control the volume and/or flow rate ofammonia drawn out of the tank 1402 by the pump 1404. The pressureregulator 1406 monitors the pressure of the liquid ammonia in the tank1402. Once the pressure lowers to a threshold pressure value whereby theliquid ammonia can vaporize into a gaseous form, the pressure regulator1406 opens and feeds gaseous ammonia downstream. Any residual liquidammonia that passes through the pressure regulator 1406 is fed to aninjection system 1408 (via, for example, a T-coupling on a supply line).

In an embodiment, a temperature control valve 1410 receives atemperature feedback signal 1412 that contains a temperature readingfrom an electric catalyst unit 1420 during a cold start of the engine.The temperature feedback signal 1412 can be generated by a temperaturesensor coupled to the electric catalyst unit 1420. Once the electriccatalyst unit 1420 reaches a threshold temperature (i.e., thetemperature reading is equal to or greater than the thresholdtemperature) suitable to perform the ammonia cracking process, thetemperature control valve 1410 opens and the gaseous ammonia passesthrough the heat exchange catalyst unit 1418, and travels downstream tothe electric catalyst unit 1420, which is heated using power suppliedfrom the vehicle power system 1422.

If the electric catalyst unit 1420 has not reached the thresholdtemperature, then the temperature control valve 1410 continues tomonitor the temperature feedback signal 1412, and prevents thedownstream travel of the gaseous ammonia. The cold start operation isdescribed in more detail herein.

In an embodiment, the temperature of the heated exhaust gas entering theheat exchange catalyst unit 1418 is judged based on the current draw inthe electric catalyst unit 1420, where the current draw is indicative ofhow effective the heat exchange catalyst unit 1418 is in cracking thegaseous ammonia.

For example, if there is hydrogen and nitrogen passing from the heatexchange catalyst unit 1418 to the electric catalyst unit 1420, theelectric catalyst unit 1420 will not perform the ammonia crackingprocess, and thus will draw minimal or no current.

If, however, gaseous ammonia passes from the heat exchange catalyst unit1418 to electric catalyst unit 1420, the ammonia cracking process willoccur, drawing current in order to heat the heating element disposedwithin the electric catalyst unit 1420.

However, during a normal or high load operating conditions of the engine(i.e., not during a cold start or low load operating conditions), theon-board ammonia cracking system 1400 does not utilize the electriccatalyst unit 1420 to perform the ammonia cracking process, and the heatexchange catalyst unit 1418 performs the ammonia cracking process as itwill have been heated to the threshold temperature by the heated exhaustgas from the engine.

The heat exchange catalyst unit 1418 referred to in FIG. 14 can be anyof the embodiments described herein—the heat exchange catalyst unit 100that utilizes a TPMS structure, the cylindrical heat exchange catalystunit 700 that utilizes a TPMS structure, the heat exchange catalyst unit1000 that utilizes a tube bundle structure, or the two-pass heatexchange catalyst unit 1300 that utilizes a tube bundle structure.

The pressure control valve 1414 is located in series with thetemperature control valve 1410, and controls the amount of gaseousammonia which is fed into the heat exchange catalyst unit 1418.

In an embodiment, the pressure control valve 1414 receives a pressurefeedback signal 1416 from the heat exchange catalyst unit 1418. Forexample, the heat exchange catalyst unit 1418 can be coupled to apressure transducer or the like (not depicted in FIG. 14 ) thatgenerates the pressure feedback signal 1416.

In an embodiment, to facilitate a cold start of the on-board ammoniacracking system 1400 when the exhaust gas from the engine is not at athreshold temperature suitable to perform the ammonia cracking process,the electric catalyst unit 1420 is used to heat the catalyst so that thegaseous ammonia can be cracked, and the resulting hydrogen is to besupplied to the downstream injection system for the engine. The enginecan then burn the hydrogen, powering the engine which results in heatedexhaust gas being supplied to the on-board ammonia cracking system 1400.

In an embodiment, the electric catalyst unit 1420 is coupled to thevehicle power system 1422, such as a traditional vehicle battery. Inanother embodiment, the electric catalyst unit 1420 can be heated via asupplemental heating/electric source, such as a renewable energy source,a portable battery source, an on-board electric battery pack, and/or arechargeable battery.

In addition to facilitating a cold start of the on-board ammoniacracking system 1400, the electric catalyst unit 1420 is utilized tosupplement the heat exchange catalyst unit 1418 during low loadoperating conditions of the engine, such as when the vehicle is stopped,moving slowly, or idling. For example, during low load operatingconditions, the engine exhaust gas temperature can drop significantly.The reduced temperature of the exhaust gas flowing into the heatexchange catalyst unit 1418 during such low load operating conditionsmay not be sufficient for the catalyst to crack the ammonia. In anembodiment, depending on the specific catalyst that is utilized, thetemperature of the exhaust gas needs to be at least 400° C. to 700° C.in order to perform the ammonia cracking process, and in a preferredembodiment, the temperature of the exhaust gas is at least 600° C. inorder to perform the ammonia cracking process.

In this scenario, the cold gaseous ammonia will pass through the heatexchange catalyst unit 1418, and will be supplied downstream to theelectric catalyst unit 1420, which is heated using power supplied fromthe vehicle power system 1422. Once the electric catalyst unit 1420 isheated to a threshold temperature suitable to perform the ammoniacracking process, the temperature control valve 1410 opens and allowsthe gaseous ammonia to be fed to the heat exchange catalyst unit 1418and ultimately to the electric catalyst unit 1420. The electric catalystunit 1420 then performs the ammonia cracking process, and the resultinghydrogen is supplied to the downstream injection system for the engine.

When the exhaust gas flowing into the heat exchange catalyst unit 1418reaches a threshold temperature suitable to perform the ammonia crackingprocess, such as during normal or high load operating conditions of theengine, the ammonia cracking process occurs within the heat exchangecatalyst unit 1418. The resulting hydrogen and nitrogen will passdownstream through the electric catalyst unit 1420, and furtherdownstream to a gas-to-liquid or gas-to-gas heat exchange unit 1428, andsubsequently to the injection system 1430 for the engine. In anembodiment, the gas-to-liquid or gas-to-gas heat exchange unit 1428 mayleverage engine coolant and/or the engine radiator, or input ammonia gasor liquid, to facilitate the heat exchange process.

In an embodiment, the pressure regulator 1406 can be controlled with anelectric servomotor to provide a steady flow of gaseous ammonia from thetank 1402. In another embodiment, a pulse-width modulated injectionvalve can be used. The servomotor and/or pulse generators can becontrolled using an electronic controller, such as an industrial PIDcontroller (not depicted in FIG. 14 ).

In an embodiment, the electronic controller can be coupled to variouscomponents of the on-board ammonia cracking system 1400 to receiveinputs from the pressure regulator 1406, the temperature control valve1410, pressure control valve 1414, as well as from sensors such astemperature sensors and pressure transducers which may be coupled to theheat-exchange catalyst unit 1418 and/or electric catalyst unit 1420.

In another embodiment, the electronic controller can be integrated intothe hardware and software with the vehicle's electronic control unit(ECU). In this embodiment, the flow rate of hydrogen fed to theinjection system of the engine can be measured and reported back to theECU as a mechanism to control the injection strategy.

FIGS. 15-17 are various perspective views of the on-board ammoniacracking system 1400 for an internal combustion engine described in FIG.14 .

FIG. 18 is a perspective view of an electric catalyst unit. In anembodiment, the electric catalyst unit 1800 comprises a housing 1802which encloses a ceramic tube 1900 (depicted in FIG. 19 ). In anembodiment, the housing 1802 is a metal housing.

In an embodiment, the electric catalyst unit 1800 includes a gaseousammonia inlet 1804 and a hydrogen outlet 1806 disposed on the oppositeend of the electric catalyst unit 1800. The electric catalyst unitfurther includes power feed-throughs 1808, 1810 for the heating element1904 (depicted in FIG. 19 ). In an embodiment, the electric catalystunit 1800 can include radial fittings 1812, 1814 that may be used for avariety of functions. For example, the radial fittings 1812, 1814 mayserve an inlets, outlets, or may be coupled to equipment fortemperature, throughput, and/or pressure sensing. In an embodiment, theradial fittings 1812 can each include, or be coupled to, thermocouples,and the radial fitting 1814 can include, or be coupled to, a pressuretransducer.

FIG. 19 is a cross-sectional view of the electric catalyst unit 1800. Inan embodiment, a ceramic tube 1900 houses a catalyst. The ceramic tube1900 acts as an insulator, and allows heat to be focused and reflectedtoward the catalyst, thereby heating the catalyst.

In an embodiment, a first screen 1901 and second screen 1902 aredisposed at opposite ends within the ceramic tube 1900. The screens1901, 1902 can be made from wire, a wire mesh, or another metallic meshor matrix structure. In an embodiment, the screens 1901, 1902 can bemade from a nickel alloy that is resistant to heated hydrogen gas thatis generated from the cracking of ammonia, as well as resistant to thegaseous ammonia itself.

In an embodiment, a heating element 1904 is also disposed within theceramic tube 1900. Electrical current is passed through the heatingelement 1904 in order to heat the heating element 1904 to a thresholdtemperature suitable to perform the ammonia cracking process. In anembodiment, the heating element 1904 and screens 1901, 1902 are madefrom a nickel alloy, or other material(s) resistant to hydrogen andammonia, as nickel maintains a fairly constant resistance with hightemperatures, as opposed to steel which has a lower resistance at hightemperatures. Further, nickel alloys may have a higher resistance tocorrosion during exposure to ammonia and hydrogen at high temperatures(which may be realized within the electrical catalyst unit 1800, suchas, for example, temperatures in excess of 600° C.).

In a preferred embodiment, the heating element 1904 and the screens1901, 1902 are made from Inconel® 625. In an embodiment, the heatingelement 1904 and the screens 1901, 1902 can be made from the samematerial. Alternatively, the heating element 1904 and the screens 1901,1902 can be made from different materials.

In an embodiment, the heating element 1904 can be an air process heater,a cartridge heater, a tubular heater, a band heater, a strip heater, anetched foil heater (or a thin-film heater), a ceramic heater, a ceramicfiber heater, a resistance wire, and the like.

In an embodiment, respective ends of the heating element 1904 are incontact with the power feed-throughs 1808, 1810. The power feed-throughs1808, 1810 provide electricity for energizing or heating the heatingelement 1904.

In an embodiment, the heating element 1904 is regulated via anelectronic controller coupled to the power feed-throughs 1808, 1810 byutilizing readings from the thermocouples coupled to the radial fittings1812, so that the heating element 1904 maintains a threshold temperaturesuitable to perform the ammonia cracking process. The thresholdtemperature can range from 400° C. to 700° C., and in a preferredembodiment, the threshold temperature is at least 600° C.

In an embodiment, the electronic controller can be used to control anelectric expansion valve (not depicted in FIG. 19 ) that is coupled tothe inlet 1804 by utilizing readings from the pressure transducercoupled to radial fitting 1814 and/or the thermocouples coupled toradial fittings 1812. Once the gaseous ammonia received by the electriccatalyst unit 1800 from the heat exchange catalyst unit has reached thethreshold temperature, the electric expansion valve is utilized tomaintain the vapor pressure of the gaseous ammonia. At these thresholdtemperature and pressure values, the electric expansion valve is opened,allowing the ammonia to enter the ceramic tube 1900.

In an embodiment, catalyst, such as discrete catalyst media, isdeposited into the ceramic tube. The gaseous ammonia undergoes achemical reaction with the catalyst disposed within the ceramic tube1900, and the resulting hydrogen and nitrogen components exit theelectric catalyst unit 1800 via the outlet 1806 and are supplied to thedownstream injection system for the engine.

In another embodiment, the heating element 1904 is coated with acatalyst that facilitates the ammonia cracking process, and discretecatalyst is not disposed within the ceramic tube 1900. In thisembodiment, the catalyst is coated to the heating element 1904 using awashcoating or deposition technique to bind or adhere the catalyst tothe surfaces of the heating element 1904.

In one embodiment, the heating element 1904 is a strip heater. Theheating element 1904 can be coated on all surfaces with the catalyst, oralternatively, a catalyst sleeve can be placed over the strip heatingelement 1904. In an embodiment, the strip heating element 1904 can havea relatively low heat transfer efficiency so as to maintain a high skin(or boundary layer) temperature of the catalyst that externally coatsthe strip heating element 1904.

In another embodiment, the heating element 1904 is a spiral heater, acoil heater, or an air process heater, where the internal walls (whichcontain integral heating elements) are coated with the catalyst.

In yet another embodiment, the catalyst is coated on the interiorwall(s) of the ceramic tube 1900. In this embodiment, the catalyst iscoated to the interior wall(s) of the ceramic tube 1900 using awashcoating or deposition technique to bind or adhere the catalyst tothe wall surfaces.

The remaining figures have been provided to show additional details andembodiments of the on-board ammonia cracking system.

While the principles of the disclosure have been illustrated in relationto the exemplary embodiments shown herein, the principles of the presentinvention are not limited thereto and include any modification,variation, or permutation thereof.

1. A system for on-board ammonia cracking for an internal combustionengine, comprising: an ammonia tank containing liquid ammonia; a heatexchange catalyst unit fluidly coupled to the ammonia tank, wherein theheat exchange catalyst unit receives exhaust gas from the internalcombustion engine; and an electric catalyst unit fluidly coupled inseries to the heat exchange catalyst unit, wherein gaseous ammonia flowsfrom the ammonia tank to the heat exchange catalyst unit uponvaporization of the liquid ammonia, wherein the gaseous ammoniaundergoes a cracking process in the heat exchange catalyst unit if theexhaust gas has reached a temperature sufficient to perform ammoniacracking, and wherein the gaseous ammonia exits the heat exchangecatalyst unit and flows to the electric catalyst unit and undergoes thecracking process in the electric catalyst unit if the exhaust gas hasnot reached a temperature sufficient to perform ammonia cracking.
 2. Thesystem of claim 1, wherein the ammonia tank is coupled to a pump.
 3. Thesystem of claim 1, wherein the electric catalyst unit includes anelectric heater.
 4. The system of claim 1, wherein the heat exchangecatalyst unit includes a matrix having a series of rows and columns. 5.The system of claim 4, wherein surfaces of the matrix are coated with acatalyst.
 6. The system of claim 1, wherein the heat exchange catalystunit includes a tube bundle structure, the tube bundle structurecomprising individual tubes which extend along the width of the heatexchange catalyst unit perpendicular to an inlet that receives theexhaust gas.
 7. The system of claim 1, wherein the temperaturesufficient to perform ammonia cracking is at least 600° C.
 8. A systemfor on-board ammonia cracking for an internal combustion engine,comprising: an ammonia tank containing ammonia; a heat exchange catalystunit fluidly coupled to the ammonia tank, wherein the heat exchangecatalyst unit receives exhaust gas from the internal combustion engineand receives the ammonia from the ammonia tank; and an electric catalystunit fluidly coupled in series to the heat exchange catalyst unit, theelectric catalyst unit including an electric heater, wherein the ammoniaundergoes a cracking process in the heat exchange catalyst unit if theexhaust gas has reached a temperature sufficient to perform ammoniacracking, wherein the ammonia exits the heat exchange catalyst unit andflows to the electric catalyst unit and undergoes the cracking processin the electric catalyst unit if the exhaust gas has not reached atemperature sufficient to perform ammonia cracking, and wherein hydrogenresulting from the cracking process flows to the internal combustionengine.
 9. The system of claim 8, wherein when the ammonia undergoes thecracking process in the heat exchange catalyst unit, resulting hydrogenand nitrogen exits the heat exchange catalyst unit and flows to theelectric catalyst unit.
 10. The system of claim 8, wherein when theammonia undergoes the cracking process in the electric catalyst unit,the ammonia has been pre-heated in the heat exchange catalyst unitbefore flowing to the electric catalyst unit.
 11. The system of claim 8,wherein the temperature sufficient to perform ammonia cracking rangesfrom 400° C. to 700° C. depending on the specific catalyst disposed inthe heat exchange catalyst unit or in the electric catalyst unit. 12.The system of claim 8, wherein the electric heater is selected from agroup consisting of an air process heater, a cartridge heater, a tubularheater, a band heater, a strip heater, an etched foil heater, athin-film heater, a ceramic heater, a ceramic fiber heater, and aresistance wire.
 13. The system of claim 8, wherein the heat exchangecatalyst unit includes a matrix having a series of rows and columns. 14.The system of claim 8, wherein the heat exchange catalyst unit includesa tube bundle structure comprising individual tubes which extend alongthe width of the heat exchange catalyst unit perpendicular to an inletfor the exhaust gas.
 15. A system for on-board ammonia cracking for aninternal combustion engine, comprising: an ammonia tank containingammonia; a heat exchange catalyst unit fluidly coupled to the ammoniatank, wherein the heat exchange catalyst unit receives exhaust gas fromthe internal combustion engine and receives the ammonia from the ammoniatank; and an electric catalyst unit fluidly coupled in series to theheat exchange catalyst unit, the electric catalyst unit powered using avehicle power system, wherein the ammonia undergoes a cracking processin the heat exchange catalyst unit if the exhaust gas has reached atemperature sufficient to perform ammonia cracking, and if the exhaustgas has not reached a temperature sufficient to perform ammoniacracking: (1) the ammonia is pre-heated in the heat exchange catalystunit, (2) the pre-heated ammonia exits the heat exchange catalyst unitand flows to the electric catalyst unit, and (3) the pre-heated ammoniaundergoes the cracking process in the electric catalyst unit.
 16. Thesystem of claim 15, wherein the electric catalyst unit includes anelectric heater.
 17. The system of claim 16, wherein the electric heateris selected from a group consisting of an air process heater, acartridge heater, a tubular heater, a band heater, a strip heater, anetched foil heater, a thin-film heater, a ceramic heater, a ceramicfiber heater, and a resistance wire.
 18. The system of claim 15, whereinthe electric catalyst unit includes discrete catalyst media depositedwithin the electric catalyst unit.
 19. The system of claim 15, whereinthe temperature sufficient to perform ammonia cracking ranges from 400°C. to 700° C. depending on the specific catalyst disposed in the heatexchange catalyst unit or in the electric catalyst unit.
 20. The systemof claim 15, wherein hydrogen resulting from the cracking process flowsto the internal combustion engine for use as a combustion co-fuel withthe ammonia.